This invention relates generally to ink jet print heads and more particularly concerns such a print head which includes a filter to prevent the introduction of particulate matter and air bubbles into the flow path to the print head nozzles.
In an ink jet print head, liquid ink is contained in the interior of an ink chamber in a print head body, usually retained within a foam material. Such print heads combine ink storage and drop ejection functions in a single package. The print head includes an ink reservoir made up of one or more chambers containing ink-saturated porous material and a print element in which electronic and fluidic components that control the ejection of ink droplets reside. Interconnection between the ink reservoir and the print element is accomplished by an ink manifold. Filter/standpipe structures, one in each reservoir chamber for each color of ink, form a part of the ink manifold.
In the past, a fine mesh filter has been affixed to the entrance of each standpipe. The filter is in intimate contact with the porous reservoir material above the standpipe, which is typically a polyurethane foam. The filter/standpipe assembly performs a number of essential functions. Since the porous reservoir material is chosen to be deformable, the filter/standpipe assembly compresses the reservoir material near the filter. This compression insures intimate contact between the filter and the reservoir material. The filter also acts as a capillary drain, allowing ink passage upon demand but preventing air passage into the standpipe. This function is enhanced by the intimate contact between the filter and the reservoir material. A proper balance between filter pore size and reservoir material compression insures a high reservoir drainage efficiency. Finally, the most obvious function of the filter is to prevent passage of contaminant particles into the print element. If contaminant particles enter the print element, they can block the tiny ink channels found in the high resolution print elements.
Foremost among the requirements of an acceptable filter bond to the standpipe is that it extend around the entire perimeter of the contact line between the filter and the standpipe. This is made difficult by the usual difference in material properties between the filter and the standpipe. In one prior ink cartridge, for example, the filter is a stainless steel wire mesh while the standpipe is a polyphenylene oxide resin. Failure to achieve a complete bond around the periphery of this standpipe with the mesh leaves a pathway for the passage of air and contaminant particles into the standpipe.
The usual technique for attaching the mesh filter onto the plastic standpipe structure is heat stake welding. This method has several drawbacks in a high volume manufacturing environment. Foremost among these drawbacks is the difficulty in reliably achieving a suitable bond between the filter and the standpipe. The heat stake welding process can be made to work reliably only after extensive optimization of multiple operating parameters. A second drawback of heat stake welding is its tendency under certain conditions to generate particulate contamination.
One alternative to heat stake welding is adhesive bonding of the mesh to the standpipe. Although this method circumvents the problem of particulate generation, the process still requires extensive optimization. In addition, the time and temperature required to cure adhesives render this alternative unattractive compared to heat stake welding.
It is an objective of the present invention to provide a cartridge assembly of the foregoing type with an improved filter/standpipe arrangement.
This objective is met in accordance with the present invention by the provision of a self-sealing elastomer filter insert which is received over the top of a standpipe in an ink chamber in an ink jet cartridge.
Advantageously, the provision of such a self-sealing elastomer filter insert eliminates the need to achieve a permanent bond between the filter and the standpipe since the filter insert seals itself against the standpipe wall.
As a further advantage, the potential for particulate generation in the assembly process is eliminated, and the assembly operation is greatly simplified, leading to more reliable assembly.
Further, contact between the porous reservoir material and the filter is, in the present form of the invention, additionally enhanced by "coining" the filter material into a domed shape. This insures adequate contact between the filter and the reservoir material and enhances reservoir draining efficiency.
Still further, the self-sealing elastomer filter may be much more easily handled than a mesh filter element during assembly of the print head.